This invention relates to methods and compositions for retarding the hardening of phenolic resole resin binder compositions which are hardened with magnesium oxide or magnesium hydroxide alone or together with an ester functional hardening agent. Such hardening can take place at about room temperature.
It is desirable to be able to easily control the rate of phenolic resole resin hardening, such as by being able to retard the hardening and maintain flowability, trowelability, and other working properties of the phenolic resin composition. This is particularly the case in warm climates and at higher temperatures.
Applicant has found that hardening of phenolic resole resins admixed with hardening quantities of lighburned magnesium oxide or magnesium hydroxide, either along or together with an ester functional hardening agent can be retarded by use of materials which decrease the solubility of magnesium ions in the mixture.
Phenolic resole resins can be room temperature hardened by several means, such as: (1) contact with a strong acid; (2) contact with an ester functional hardening agent, particularly when the phenolic resole resin is highly alkaline; (3) contact with alkaline earth oxides or hydroxides such as calcium or magnesium oxides or hydroxides; (4) gassing of certain phenolics with chemicals such as amines; and (5) hardening with both a magnesium oxide or hydroxide hardening agent and an ester functional hardening agent. Use of strong acids is unsatisfactory because a basic filler is generally used in binder compositions and this causes the acid to be neutralized and become ineffective. Furthermore, strong acids can be corrosive. The amine and other gasing agents are generally toxic. Use of ester functional curing agents at a high pH (greater than about 12), which often serve as binders for foundry applications such as shaped foundry cores and molds, present problems because of the high alkalinity and alkali metal content such as that of sodium or potassium. The high pH causes concern for handling and final disposal to the environment. The high potassium or sodium concentrations are undesirable for certain uses such as that in polymer concrete or thermal bonding of glass or polyester fibers since high concentrations of alkali metals at a high pH lead to attack of such materials.
Lightburned magnesium oxide and magnesium hydroxide are well known room temperature (R.T.) hardening agents for phenolic resole resins. Furthermore, magnesium oxide and magnesium hydroxide are often used as the condensation catalysts for the manufacture of phenolformaldehyde resole resins from phenol and formaldehyde. Additionally, relatively inactive magnesia, e.g., periclase, is a conventional refractory aggregate which is often bound into various shapes with phenolic resins. Illustrative of references which disclose the use of magnesium oxide or magnesium hydroxide to harden phenolic resole resins in various types of compositions, there can be mentioned U.S. Pat. Nos. 2,869,194 of Jan. 20, 1959 to R. H. Cooper; 2,869,196 of Jan. 20, 1959 to R. H. Cooper; 2,913,787 of Nov. 24, 1959 to R. H. Cooper; 3,666,703 of May 30, 1972 to T. Murata et al; 2,712,533 of Jul. 5, 1955 to J. S. Mitchell; 2,424,787 of Jul. 29, 1947 to W. H. Adams, Jr.; and 4,794,051 of Dec. 27, 1988 to M. K. Gupta. The 4,794,051 Gupta patent also mentions the use of a class of ester functional hardening agents namely, lactones, which are used together with the magnesium hardeners, but preferably in admixture with calcium hardener. The U.S. Pat. No. 2,869,194 Cooper patent also mentions that magnesium oxychloride and magnesium oxysulate, which can be prepared by mixing magnesium oxide powder with an aqueous solution of magnesium chloride or its equivalent or magnesium sulfate or its equivalent, frequently provide shorter hardening times as compared to the magnesium oxide alone.
U.S. patent application Ser. No. 450,989 entitled "Phenolic Resin Compositions" filed Dec. 15, 1989 with P. H. R. B. Lemon, J. King, H. Leoni, G. Murray, and A. H. Gerber as inventors, which is based on GB 8829984.7 filed 12/22/88, discloses the preparation of phenolic resole resins with alkali or alkaline earth metal compounds as the basic catalyst and the subsequent room temperature hardening of such resins with an esterified phenolic resole as the ester functional hardening agent together with various bases, including oxides and hydroxides of magnesium and calcium.
European patent application Publication No. 0094165, which was published on Nov. 16, 1983 with P. H. R. B. Lemon et al as inventors, has broad recitations which mention the use of various alkaline materials including magnesium oxide (magnesia) for condensing phenol and formaldehyde to form phenol-formaldehyde resins and for further increasing the alkalinity of such resins which use ester functional agents for hardening the phenolic resin. European patent application Publication No. 0243,172, which was published on Oct. 28, 1987 and lists P. H. R. B. Lemon et al as inventors, has recitations similar to those of the above-mentioned 0094165 publication.
U.S. patent application Ser. No. 288,090, which was filed on Dec. 22, 1988 with A. H. Gerber as inventor, discloses the use of lithium ion generating alkalizing agents in resole resin binder compositions which, when hardened by an ester functional hardening agent, exhibit tensile and compressive strengths superior to that obtained from compositions using sodium or potassium ion generating alkalizing agents.
U.S. Pat. No. 4,011,186 of Mar. 8, 1977 to Higgenbottom as well as U.S. Pat. No. 4,216,295 of Aug. 5, 1980 to Dahms relate to phenolic resoles catalyzed with alkaline earth metal hydroxides and neutralized with oxalic acid or its acid salts which provide stable, inert, insoluble oxalate salts dispersed in said resole and, additionally increases the viscosity of the resole resin.
U.S. Pat. No. 3,624,247 of Nov. 30, 1971 to Gladney et al relates to the removal of residual calcium catalyst used in the production of phenolic resins. The residual calcium catalyst is removed by treatment with an alkaline solution of an ammonium salt which forms an insoluble salt with calcium upon pH adjustment. Soluble ammonium compounds used in the process of the 247 patent are listed as sulfate, phosphate, and carbonate.
U.S. Pat. Nos. Re. 32,720 of Jul. 26, 1988 and Re. 32,812 of Dec. 27, 1988 to P. H. R. B. Lemon et al are further illustrative of the literature which discloses room temperature hardening of highly alkaline phenol-formaldehyde resole resins with an ester curing agent. U.S. patent application Ser. No. 149,102 which was filed on Jan. 27, 1988 to Detlefsen et al shows the use of aliphatic alcohols to moderate or retard the hardening of phenolic resole resins with ester functional hardening (curing) agents.